1. Field of the Invention
The present invention relates to an image forming device, and more particularly, to an image forming device in which an engine control unit, which has a video unit to convert data into image data, and an engine mechanism to perform a data printing process, are driven with a single processor.
2. Description of the Related Art
Generally, an electrophotographic image forming device such as a laser printer, an LED printer, a facsimile, or a digital copier, performs a series of image forming processes to print image data from a computer or a scanner into a visual image on a printing medium such as a paper sheet. These image forming processes will be described in greater detail below with reference to FIG. 1.
FIG. 1 is a block diagram schematically showing a conventional laser printer. Referring to FIG. 1, the conventional laser printer includes a video unit 10 and an engine unit 30.
The video unit 10 includes an operation panel 11, a computer I/F unit 12, a memory unit 13, a video I/F unit 14, and a CPU 15. The operation panel 11 includes an input unit (not shown) having a plurality of keys to input commands, and a display unit (not shown) to display an operational status of the laser printer. The computer I/F unit 12 is connected between a host computer and the CPU 15 to interface an input/output signal. The memory unit 13 includes a ROM (not shown) to store a control program and various application programs to drive the video unit 10, and a RAM (not shown) to temporarily store various data input from the host computer. The video I/F unit 14 is connected between the CPU 15 and the engine unit 30 and interfaces the input/output signal. The CPU 15 controls the overall operation of the video unit 10 in accordance with the control program stored in the memory unit 13. Data, control and address busses connect the memory unit 13 and the CPU 15.
The CPU 15 generates a display list to generate frame data from the data transmitted from the host computer via the computer I/F unit 12, color corrects to YMCK (yellow, magenta, cyan, black) color format and stores the color corrected data in the memory unit 13. The CPU 15 generates the data stored in the memory unit 13 into frame data of bitmap format of respective colors, and transmits the generated data to the engine unit 30 through the video I/F unit 14.
The engine unit 30 includes a CPU 31 to control driving of an engine mechanism 40 under the control of the video unit 10, and a memory unit 33 having a ROM (not shown) to store various control programs and a RAM (not shown) to temporarily store data from the execution of the programs by the CPU 31. Data, control and address busses connect the memory unit 33 and the CPU 31. The engine unit 30 further includes an engine I/F unit 32 connected between the video I/F unit 14 and the CPU 31 to interface the input/output signal, and an engine mechanism 40 to perform printing processes under the control of the CPU 31. The engine mechanism 40 includes a paper feeding unit 41, a laser scanning unit (LSU) driving unit 42, an LSU 42a, a developing unit 43, a transfer unit 44, a fusing unit 45 and a sensing unit 46.
Describing the controlling of the CPU 31 in detail, first, as a printing start command is received from the video unit 10 through the engine I/F unit 32, the CPU 31 controls the paper feeding unit 41 so that a sheet of printing paper is picked up. When the picked up paper sheet is determined to have reached a predetermined reference position as a result of sensing by the sensing unit 46, the CPU 31 transmits a page synchronization (Psync) signal to the video unit 10 through the engine I/F unit 32, to thus notify that the printing is started. Accordingly, as bitmap data is received from the video unit 10 in response to the Psync signal, the CPU 31 controls the engine mechanism 40 so that the printing with respect to the received bitmap data is performed.
As described above, the conventional laser beam printer has a separate video unit 10 and engine unit 30, and thus requires separate CPUs 15 and 31. This results in a complicated system, thus it is not easy to diagnose or recover the system in the event of error. Further, the I/F units 14 and 32 are also required to interface between the video unit 10 and the engine unit 30.
In order to construct the I/F units 14 and 32, various physical channels are required such as a command bus, an address bus, a status information bus, a data bus and a control bus, each including plural bits. In this case, because a plural number of pins among the pins of the respective CPUs 15 and 31 are used for the construction of the I/F units 14 and 32, usually, a serial bus such as a serial input/output (SIO), or the universal asynchronous receiver/transmitter (UART) is used. However, with the serial bus, the data transmission rate is slower than when using the parallel bus, and thus it is inefficient for the high speed data transmission.
Further, because a plural number of I/O ports, connectors and harnesses are required to construct the interface, the material costs increase, subsequently increasing the manufacturing costs.